Ashley Madison is sending out copyright takedown notices in a failed attempt to stop the spread of stolen data

Hacked extramarital dating service Ashley Madison is trying to prevent dissemination of its stolen database by sending copyright takedown notices to social networks and file-sharing sites.

The action, after 33m user records were posted online, mirrors the largely successful attempt to get an earlier, smaller, leak of user data scrubbed from the internet. But this time, the main dump remains very much online, as the arms race between hackers and hacked has escalated to include the use of technology such as peer-to-peer file sharing protocol bittorrent and the anonymous browsing service Tor.

Ashley Madison has had some success in taking down links from centralised services such as Twitter or Facebook. Some tweets containing links to the dump have been removed from the service, while a Reddit subforum devoted to sharing the dump was removed almost immediately by the site (A second subreddit has been allowed to stand, but only by promising not to share direct links to the data).

Ashley Madison has also been accused of being overzealous with its enforcement. Joseph Cox, a writer for tech site Motherboard, reported that a copyright takedown notice was filed for three of his tweets, each of which contained screenshots of information contained within the Ashley Madison breach.

Twitter took down one tweet, which contained an image of the company's floor plan. But the company disagreed with Ashley Madison over the infringing nature of the other two tweets, Cox writes. "One was a heavily censored screenshot of a spreadsheet which details the shareholders of the company and the percentile of shares they own. The screenshot did not include any names, figures, or other data, but simply the headers of two columns. Another screenshot showed the column headers of a spreadsheet detailing the company's bank accounts."

The main dump is hosted on a Tor "hidden service" - a website which can only be accessed through the anonymous browser. Unlike a normal website, which visitors connect to directly, a hidden service is accessed via an encrypted connection routed through third-parties which obscure the website's address from its visitors, and vice-versa. That means that it's very difficult to use the legal system to take down the main dump, since no-one yet knows who to send the takedown notices too.

On top of that, the dump itself is now being disseminated using bittorrent, a peer-to-peer transfer protocol. The file is broken up into multiple blocks, which are then shared directly from one downloader's computer to the next. With no central repository, it is all but impossible to prevent the transfer, although a "magnet" link - a short string of text telling a new downloader how to connect to the "swarm" of files - is still required.